You have a horizontal grindstone (a disk) that is 94 kg, has a 0.31 m radius, is turning at 86 rpm (in the positive direction), and you press a steel axe against the edge with a force of 15 N in the radial direction. F - - 4 50% Part (a) Assuming that the kinetic coefficient of friction between steel and stone is 0.20, calculate the angular acceleration of the grindstone in rad/s. A 50% Part (b) What is the number of turns, N, that the stone will make before coming to rest? N =